1. Field of the Invention
The present invention relates to an improved etching method for improving the adhesiveness of a photoresist film employed in a photo etching process.
2. Description of the Related Art
Proper etching techniques for photoetching processes are very important in the manufacture of semiconductor devices.
In a prior photoetching process, the use of a positive resist material has been expected to form patterns with accuracy. However, it has been difficult to obtain an etching mask with satisfactory accuracy since the positive resist material has been inferior in adhesiveness to the material to be patterned.
In particular, when the material to be etched is phosphorus silica glass (PSG), the adhesiveness of the positive resist film to the phosphorus glass film is poor. As a result, there has been often produced semiconductor materials which are underetched and which resist peeling.
This phenomenon has been described as follows: The PSG film generally possesses a tetrahedral structure of SiO.sub.4, on the surface of which a silanol group layer or a siloxane group layer is formed. This layer has properties which make it likely to adsorb moisture in air and form an adsorbed water layer, hydrogen bouded to the PSG surface. This adsorbed water layer repels organic solvents and deteriorates in its adhesiveness to a positive resist material.
Such adsorbed water can be instantaneously dehydrated by baking. However, it has been difficult to maintain this moisture removal effect over a long period of time, since it rapidly absorbed moisture in the atmosphere because of the presence of silanol groups and siloxane groups.
Conventionally, there has been known a method to overcome such a difficulty wherein after the PSG substrate surface is coated with a material to improve the adhesiveness, for example, an HMDS (hexamethyl disilazane) organic solvent is employed and a positive resist film is formed. This method however has not offered sufficient effect.